Terminal component, secondary battery, and method for producing the terminal component

The present disclosure relates to a terminal, a secondary battery, and a method for producing the terminal. The present application claims priority based on Japanese Patent Application No. 2021-085553 filed on May 20, 2021, and the entire contents of the patent application are incorporated herein by reference.

A technology of performing plating on a portion of a terminal member in order to increase weldability of a metal member forming a terminal for a secondary battery has been disclosed.

Japanese Laid-open Patent Publication No. 2014-017081 discloses a negative electrode terminal member including a negative electrode external terminal plate with a metal plated layer formed thereon and a negative electrode connection terminal. The negative electrode external terminal plate is disposed on a battery lid and is connected to a bus bar. The negative electrode external terminal plate includes a through hole. The negative electrode connection terminal passes through the through hole and is caulked via the metal plating layer. According to the above-described configuration, an adhesion between the negative electrode terminal plate and the negative electrode connection terminal can be increased, and a connection resistance can be reduced.

Japanese Translation of PCT International Application No. 2013-519213 discloses a soft package lithium battery tab material obtained by plating a nickel-plated layer on one side surface of a base and further plating a tin-plated layer on the nickel-plated layer. It is considered that the soft package lithium battery tab material has low production cost, high weldability, and suitable heat conductivity.

Incidentally, the present inventor has examined use of a terminal component firmed of dissimilar metals as an external terminal for a secondary battery. In a case where a secondary battery is used for a vehicle, traveling vibrations of the vehicle is transmitted to an external terminal of the secondary battery via a bus bar. In a case where the external terminal is formed of a plurality of metals, the vibrations are transmitted to a joining interface between the metals. The present inventor wants to propose a terminal component in which, even when an external force, such as vibrations or the like, is transmitted, a joining interface between the metals is maintained and a durability of which is high.

A terminal component disclosed herein includes a first metal, and a second metal stacked on the first metal. On the first metal, nickel is plated at least on a boundary surface with the second metal. A joining portion joined by diffusion of the metals is formed in a portion of a boundary between the first metal and the second metal.

In the terminal component, the joining portion having a high joint strength is formed and an improved durability is achieved.

The joining portion may be formed to include a center position of the boundary surface.

In the first metal, an average thickness of nickel plating of the joining portion may be equal to or less than an average thickness of nickel plating of the boundary surface.

The second metal may include a recessed portion having an inner portion larger than an opening in a portion in which the second metal is stacked on the first metal. The first metal may have a portion that has entered the recessed portion.

In a secondary battery including a battery case and an electrode terminal mounted on the battery case, the electrode terminal may include a portion formed of the terminal component described above.

A method for producing a terminal component disclosed herein includes steps of preparing a first metal, preparing a second metal, and electrically connecting the first metal and the second metal and joining a portion of a boundary between the first metal and the second metal. On the first metal, nickel is plated on a boundary surface with the second metal.

In accordance with the above-described production method, a joining strength of a joining portion joined by diffusion of the metals can be increased.

In the first metal, a joining planned portion that is joined to the second metal may be set. An average thickness of nickel plating of the joining planned portion may be equal or less than an average thickness of nickel plating of the boundary surface.

The joining planned portion may be set to include a center position of the boundary surface.

The step of preparing the first metal may include plating nickel on the first metal by electroplating.

The step of preparing the first metal may include partially reducing a thickness of the nickel plating by polishing or laser irradiation.

One embodiment of a terminal component and a secondary battery disclosed herein will be described below. As a matter of course, the embodiment described herein is not intended to be particularly limiting the present disclosure. The present disclosure is not limited to the embodiments described herein, unless specifically stated otherwise. The accompanying drawings are schematic and do not necessarily reflect actual members or portions. Members/portions that have the same effect will be denoted by the same sign as appropriate and the overlapping description will be omitted. The notation “A to B” or the like that indicates a numerical range means “A or more and B or less” unless specifically stated otherwise. Dimension relations (length, width, thickness, or the like) in the drawings do not necessarily reflect actual dimensional relations.

As used herein, a term “secondary battery” refers to overall storage devices in which charge carriers move between a pair of electrodes (a positive electrode and a negative electrode) via an electrolyte and thus a charging and discharging reaction occurs. Such secondary batteries include not only so-called storage batteries, such as a lithium-ion secondary battery, a nickel hydrogen battery, a nickel cadmium battery, or the like, but also capacitors, such as an electric double-layered capacitor or the like. Among the above-described secondary batteries, an embodiment in which a lithium-ion secondary battery is a target will be described below.

<Lithium-Ion Secondary Battery>

is a partial cross-sectional view of a lithium-ion secondary battery. In, a state where an inside of the lithium-ion secondary batteryis exposed along a broad width surface on one side of a battery casehaving an approximately rectangular parallelepiped shape is illustrated. The lithium-ion secondary batteryillustrated inis a so-called sealed battery.is a cross-sectional view illustrating a cross section taken along the line II-II of. In, a partial cross-sectional view in a state where the inside of the lithium-ion secondary batteryis exposed along a narrow width surface on one side of the battery casehaving an approximately rectangular parallelepiped shape is schematically illustrated.

As illustrated in, the lithium-ion secondary batteryincludes an electrode body, the battery case, a positive electrode terminal, and a negative electrode terminal(also referred to as electrode terminalsand).

<Electrode Body>

The electrode bodyis housed in the battery casein a state where the electrode bodyis covered by an insulation film (not illustrated) or the like. The electrode bodyincludes a positive electrode sheetas a positive element, a negative electrode sheetas a negative electrode element, and separator sheetsandas separators. Each of the positive electrode sheet, the first separator sheet, the negative electrode sheet, and the second separator sheetis a long band-like member.

The positive electrode sheetis configured such that a positive electrode active material layercontaining a positive electrode active material is formed on each of both surfaces on a positive electrode current collecting foil(for example, an aluminum foil) having preset width and thickness excluding an unformed portionset to have a uniform width in an end portion on one side in a width direction. For example, in a lithium-ion secondary battery, the positive electrode active material is a material, such as a lithium transition metal compound material, that releases lithium ions during charging and absorbs lithium ions during discharging. In general, various other materials than the lithium transition metal compound material have been proposed for positive electrode active materials, and there is no particular limitation on the positive electrode active material used herein.

The negative electrode sheetis configured such that a negative electrode active material layercontaining a negative electrode active material is formed on each of both surfaces on a negative electrode current collecting foil(a copper foil herein) having preset width and thickness excluding an unformed portionset to have a uniform width in an end portion on one side in the width direction. For example, in a lithium-ion secondary battery, the negative electrode active material is a material, such as natural graphite, that absorbs lithium ions during charging and releases lithium ions absorbed during charging during discharging. In general, various other materials than the natural graphite have been proposed for negative electrode active materials, and there is no particular limitation on the negative electrode active material used herein.

For each of the separator sheetsand, for example, a porous resin sheet which has a required heat resistance and through which an electrolyte can pass is used. Various proposals have been made for the separator sheetsand, and there is no particular limitation on the separator sheetsand.

Herein, the negative electrode active material layeris formed, for example, to have a width larger than that of the positive electrode active material layer. Each of the separator sheetsandhas a width larger than that of the negative electrode active material layer. The unformed portionof the positive electrode current collecting foiland the unformed portionof the negative electrode current collecting foilare disposed to face opposite directions away from each other. The positive electrode sheet, the first separator sheet, the negative electrode sheet, and the second separator sheetare stacked in this order and are wound such that directions thereof are aligned to a long-side direction. The negative electrode active material layercovers the positive electrode active material layerwith the separator sheetsandinterposed between the negative electrode active material layerand the positive electrode active material layer. The negative electrode active material layeris covered by the separator sheetsand. The unformed portionof the positive electrode current collecting foilprotrudes from one side of the separator sheetsandin the width direction. The unformed portionof the negative electrode current collecting foilprotrudes from the separator sheetsandat an opposite side in the width direction.

As illustrate in, the above-described electrode bodyis formed to be flat along a single plane including winding axis to be housed in a case bodyof the battery case. The unformed portionof the positive electrode current collecting foilis disposed on one side along the winding axis of the electrode bodyand the unformed portionof the negative electrode current collecting foilis arranged on an opposite side.

<Battery Case>

As illustrated in, the battery casehouses the electrode bodytherein. The battery caseincludes the case bodyhaving an approximately rectangular parallelepiped shape with an opening on one side surface and a lidattached to the opening. In this embodiment, from a view point of reducing a weight and ensuring a required rigidity, each of the case bodyand the lidis formed of aluminum or an aluminum alloy mainly containing aluminum.

<Case Body

The case bodyhas an approximately rectangular parallelepiped shape with an opening on one side surface. The case bodyhas an approximately rectangular bottom surface portion, a pair of broad width surface portionsand(see), and a pair of narrow width surface portionsand. Each of the pair of broad width surface portionsandrises from a corresponding longer side of the bottom surface portion. Each of the pair of narrow width surface portionsandrises from a corresponding shorter side of the bottom surface portion. An openingsurrounded by the pair of broad width surface portionsandand the pair of narrow width surface portionsandis formed in one side surface of the case body

<Lid

The lidis attached to the openingof the case bodysurrounded by longer sides of the pair of broad width surface portionsand(see) and shorter sides of the pair of narrow width surface portionsand. A peripheral portion of the lidis joined to an edge of the openingof the case body. The above-described joining may be achieved, for example, by continuous welding without any gap. Such welding can be realized, for example, by laser welding.

In this embodiment, the positive electrode terminaland the negative electrode terminalare mounted on the lid. The positive electrode terminalincludes an internal terminaland an external terminal. The negative electrode terminalincludes an internal terminaland an external terminal. Each of the internal terminalsandis mounted on an inside of the lidvia an insulator. Each of the external terminalsandis mounted on an outside of the lidvia a gasket. Each of the internal terminalsandextends inside the battery case. The internal terminalof the positive electrode is connected to the unformed portionof the positive electrode current collecting foil. The internal terminalof the negative electrode is connected to the unformed portionof the negative electrode current collecting foil

The unformed portionof the positive electrode current collecting foiland the unformed portionof the negative electrode current collecting foilin the electrode bodyare mounted on the internal terminalsandeach being mounted on a corresponding one of both side portions of the lidin a longitudinal direction, respectively, as illustrated in. The electrode bodyis housed in the battery caseso as to be mounted on the internal terminalsandeach being mounted on the lid. Note that, herein, a wound type electrode bodyis illustrated as an example. A structure of the electrode bodyis not limited to the above-described structure. The structure of the electrode bodymay be, for example, a stacked structure in which a positive electrode sheet and a negative electrode sheet are alternately stacked via a separator sheet therebetween. A plurality of electrode bodiesmay be housed in the battery case.

The battery casemay be configured to house an unillustrated electrolytic solution with the electrode body. As the electrolytic solution, a nonaqueous electrolytic solution obtained by dissolving a supporting salt into a non-aqueous solvent may be used. Examples of the non-aqueous solvent include a carbonate base solvent, such as ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, or the like. Examples of the supporting salt include a fluorine-containing lithium salt, such as LiPFor the like.

is a cross-sectional view taken along the line III-III of. In, a cross section of a portion in which the negative electrode terminalis mounted on the lidis illustrated. In this embodiment, a member obtained by joining dissimilar meals is used for the external terminalof the negative electrode. In, a structure of the dissimilar metals forming the external terminal, an interface of the dissimilar metals, and the like are not illustrated and a cross-sectional shape of the external terminalis schematically illustrated.

As illustrated in, the lidincludes a mounting holeused for mounting the external terminalof the negative electrode. The mounting holepasses through the lidin a preset position of the lid. The internal terminaland the external terminalof the negative electrode are mounted in the mounting holeof the lidwith the gasketand the insulatorinterposed therebetween. At an outside of the mounting hole, a stepto which the gasketis attached is provided around the mounting hole. A seating surfaceon which the gasketis disposed is provided on the step. A protrusionused for positioning the gasketis provided on the seating surface.

As illustrated in, the external terminalof the negative electrode includes a head portion, a shaft portion, and a caulking piece. The head portionis a portion disposed on the outside of the lid. The head portionis an approximately flat plate-like portion larger than the mounting hole. The shaft portionis a portion mounted in the mounting holevia the gasket. The shaft portionprotrudes downward from an approximately center portion of the head portion. As illustrated in, the caulking pieceis a portion caulked to the internal terminalof the negative electrode inside the lid. The caulking pieceextends from the shaft portion, is bent after being inserted in the lid, and is caulked to the internal terminalof the negative electrode.

<Gasket>

As illustrated in, the gasketis a portion mounted on the mounting holeand the seating surfaceof the lid. In this embodiment, the gasketincludes a seating portion, a boss portion, and a side wall. The seating portionis a portion attached to the seating surfaceprovided on an outer surface of the lidaround the mounting hole. The seating portionincludes an approximately flat surface in accordance with the seating surface. The seating portionincludes a recess corresponding to the protrusionof the seating surface. The boss portionprotrudes from a bottom surface of the seating portion. The boss portionhas an outer shape along an inner surface of the mounting holeto be mounted in the mounting hole. An inner surface of the boss portionis an attaching hole to which the shaft portionof the external terminalis attached. The side wallrises upward from a peripheral edge of the seating portionand extends upward. The head portionof the external terminalis attached to a portion of the gasketsurrounded by the side wall

The gasketis disposed between the lidand the external terminalto ensure insulation between the lidand the external terminal. The gasketensures airtightness of the mounting holeof the lid. In view of the foregoing, a material excellent in chemical resistance and weather resistance may be used. In this embodiment. PEA is used for the gasket. PFA is a tetrafluoroethylene-perfluoroalkylvinylether copolymer. Note that a material used for the gasketis not limited to PFA.

<Insulator>

The insulatoris a portion attached to the inside of the lidaround the mounting holeof the lid. The insulatorincludes a base portion, a hole, and a side wall. The base portionis a portion disposed along the inner surface of the lid. In this embodiment, the base portionis an approximately flat plate-like portion. The base portionis disposed along the inner surface of the lidand has a size with which the base portiondoes not protrude from the lidto be accommodated in the case body. The holeis a hole provided to correspond to the inner surface of the boss portionof the gasket. In this embodiment, the holeis provided in an approximately center portion of the base portion. A stepthat is recessed is provided around the holeon a side surface opposed to the inner surface of the lid. A tip end of the boss portionof the gasketattached to the mounting holeis accommodated in the stepwithout interference. The side wallrises from a peripheral edge portion of the base portionand extends downward. A base portionprovided at one end of the internal terminalof the negative electrode is accommodated in the base portion. The insulatoris provided inside the battery case, and therefore, may have a required chemical resistance. In this embodiment, PPS is used for the insulator. PPS is poly phenylene sulfide resin. Note that a material used for the insulatoris not limited to PPS.

The internal terminalof the negative electrode includes the base portionand a connection piece(seeand). The base portionis a portion attached to the base portionof the insulator. In this embodiment, the base portionhas a shape corresponding to an inside of the side wallaround the base portionof the insulator. The connection pieceextends from one end of the base portion, further extends in the case body, and is connected to the unformed portionof the negative electrode of the electrode body(seeand).

In this embodiment, the boss portionis attached to the mounting holeand the gasketis mounted on the outside of the lid. The external terminalis attached to the gasket. At this time, the shaft portionof the external terminalis inserted through the boss portionof the gasketand the head portionof the external terminalis disposed on the seating portionof the gasket. The insulatorand the negative electrode terminalare mounted on the inside of the lid. As illustrated in, the caulking pieceof the external terminalis bent to be caulked to the base portionof the negative electrode terminal. The caulking pieceof the external terminaland the base portionof the negative electrode terminalmay be partially joined together by welding or metal joining in order to improve conductivity.

Incidentally, in the internal terminalof the positive electrode of the lithium-ion secondary battery, a required level of oxidation reduction resistance is not as high as that in the positive electrode. In view of the required oxidation reduction resistance and reduction in weight, aluminum can be used for the internal terminalof the positive electrode (see). In contrast, in the internal terminalof the negative electrode, a required level of oxidation reduction resistance is higher than that in the positive electrode. In view of the foregoing, copper is used for the internal terminalof the negative electrode. On the other hand, in the bus bar to which the external terminalis connected, in view of reduction in weight and cost cut, aluminum or an aluminum alloy can be used.

The present inventor has examined use of different types of metals in a portion connected to the internal terminaland a portion connected to the bus bar. That is, the present inventor has examined use of a metal having high weldability for the portion connected to the bus bar and the portion connected to the internal terminalin the external terminal. However, in findings of the present inventor, there are problems regarding conductivity and joining strength in dissimilar metal joining. The present inventor has examined mechanically fastening metals and metallurgically joining in order to ensure conduction between metals.